The present invention is directed toward heat exchangers, and particularly toward high pressure heat exchangers.
As is well known, discharge of refrigerants into the atmosphere is considered to be a major cause of the degradation of the ozone layer. While refrigerants such as HFC's are certainly more environmentally friendly than refrigerants such as CFC's which they replaced, they nonetheless are undesirable in that they may contribute to the so-called greenhouse effect.
Both CFC's and HFC's have been used largely in vehicular applications where weight and bulk are substantial concerns. If a heat exchanger in an automotive air conditioning system is too heavy, fuel economy of the vehicle will suffer. Similarly, if it is too bulky, not only may a weight penalty be involved, but the design of the heat exchanger may inhibit the designer of the vehicle in achieving an aerodynamically “slippery” design that would also improve fuel economy.
Refrigerant leakage to the atmosphere occurs from vehicular air-conditioning systems because the compressor cannot be hermetically sealed as in stationary systems, typically requiring rotary power via a belt or the like from the engine of the vehicle. Consequently, it is desirable to provide a refrigeration system for use in vehicular applications wherein any refrigerant that escapes to the atmosphere would not be as potentially damaging to the environment and wherein system components remain small and lightweight so as to not have adverse consequences on fuel economy.
These concerns have led to consideration of transcritical CO2 systems for use in vehicular applications. For one, the CO2 utilized as a refrigerant in such systems could be claimed from the atmosphere at the outset with the result that if it were to leak from the system in which it was used back to the atmosphere, there would be no net increase in atmospheric CO2 content. Moreover, while CO2 is undesirable from the standpoint of the greenhouse effect, it does not affect the ozone layer and would not cause an increase in the greenhouse effect since there would be no net increase in atmospheric CO2 content as a result of leakage.
However, transcritical systems typically involve very high pressures on the refrigerant side, and therefore heat exchangers used in such systems must be able to withstand such pressures, preferably (particularly in automotive systems) without significantly increasing size and weight.
U.S. Pat. No. 5,875,837 discloses a heat exchanger with serpentine tubes interleaved with flattened plate-like tubes, there being cross flow between the serpentine tube runs and the plate-like tubes. The plate-like tubes define a plurality of discrete flow paths which are open at the tube ends, the tube ends being connected by a header plate and header tank assemblies. It is desirable to facilitate assembly of such heat exchangers. Further, heat exchangers of this design may not be readily adapted for concurrent and countercurrent flow between the separate flow paths of the two tubes.